That patient told her doctor that she had purchased a tapeworm on the Internet and swallowed it. The physician called the Iowa Department of Public Health to ask what to do for her. The department's medical director, Dr. Patricia Quinlisk, advised an anti-worm medication.

Quinlisk recounted the incident Thursday in a weekly e-mail to public health workers around the state. She noted that websites have been selling tapeworms as a weight-loss tool and warned against the practice.

"Ingesting tapeworms is extremely risky and can cause a wide range of undesirable side effects, including rare deaths," she wrote. "Those desiring to lose weight are advised to stick with proven weight loss methods - consuming fewer calories and increasing physical activity."

Tapeworms are parasites that can live in the intestines of animals and humans. They can be ingested accidentally in undercooked meat. Two tapeworm species usually have mild symptoms - abdominal pain, loss of appetite, upset stomach and diarrhea - but infections from a pork tapeworm,Taenia solium,can cause seizures, so it's important to seek treatment, according to the Centers for Disease Control and Prevention.

One tapeworm can't absorb enough food and nutrients to make a big difference in weight, according to scientific research. But the parasite can cause anemia and malnutrition.

Another problem: One tapeworm can grow up to 30 feet long. And because a tapeworm has both male and female reproductive systems, a woman who starts out with one worm could be spreading a bunch of fertilized worm eggs every time she goes to the bathroom.

A century ago, hucksters often sold tapeworm eggs in pill form as a weight-loss aid, Quinlisk said. (The image below is a tapeworm species that often infects dogs.)